| Succession: | Duke of Saxe-Weimar |
| Reign: | 1683 - 1707 |
| Predecessor: | Johann Ernst II |
| Successor: | Ernst August I |
| Spouse: | Sophie Auguste of Anhalt-Zerbst Charlotte Dorothea Sophia of Hesse-Homburg |
| Issue: | Prince Johann Wilhelm, Hereditary Duke of Saxe-Weimar Ernst August I Princess Eleonore Christiane Princess Johanna Auguste Princess Johanna Charlotte Prince Karl Frederick Prince Johann Ernst Princess Marie Luise Princess Christiane Sophie |
| House: | House of Wettin |
| Father: | Johann Ernst II, Duke of Saxe-Weimar |
| Mother: | Christine Elisabeth of Schleswig-Holstein-Sonderburg |
| Birth Date: | 22 June 1664 |
| Birth Place: | Weimar |
| Death Place: | Weimar |
John Ernest III (22 June 1664 in Weimar – 10 May 1707 in Weimar), was a duke of Saxe-Weimar.
He was the second son of Johann Ernst II, Duke of Saxe-Weimar, and Christine Elisabeth of Schleswig-Holstein-Sonderburg.
After the death of his father in 1683, he inherited the duchy of Saxe-Weimar with his older brother Wilhelm Ernst as co-ruler (Mitherr).
Johann Ernst was an alcoholic; this, and his non-interest in the government, was taken advantage of by his brother, who became the only, autocratic, ruler of the duchy. However, until the time of his death, Johann Ernst served as co-duke, without any significant influence on the government.
In the first half of 1703, Johann Sebastian Bach served as a court musician at Weimar. He was still in his teens and developing a reputation as an organist. Little is known of his precise role (he may have been taken on as a violinist rather than a keyboardist), but as a mere musician, he most likely was considered a servant.[1] He left to take up a position as organist of a church at Arnstadt.
Bach returned to Weimar in 1708, after Johann Ernst's death, as court organist. Bach worked with one of Johann Ernst's sons, also called Johann Ernst, who had a keen interest in music. The prince's interest in collecting music was sufficiently well known that in 1713, when one of Bach's pupils, P. D. Kräuter, was requesting leave of absence to study in Weimar, he mentioned the French and Italian music that the prince was expected to introduce there.[2] The prince also composed, and Bach wrote the Organ Concerto No.1 in G Major, BWV 592, and Concerto for Organ solo in C major, BWV 595, after a theme by the prince.[3]
In Zerbst on 11 October 1685 Johann Ernst married firstly Sophie Auguste of Anhalt-Zerbst. They had five children:
In Kassel on 4 November 1694 and only two months after the death of his first wife, Johann Ernst married secondly Charlotte Dorothea Sophia of Hesse-Homburg. They had four children:
After Johann Ernst's death, his successor and eldest son, Ernst August, was nominally given his father's power, but the real power was retained by his uncle, Wilhelm Ernst, until his death in 1728, when Ernst August became the sole reigning duke of Saxe-Weimar.